Field of the Invention
The invention relates to a lock for closing an entry point of a circumferential slot that is undercut on both sides and is intended for accommodating blade roots of moving blades of a turbine rotor, wherein a filling piece has a contour adapted to the blade roots and is supported against a supporting side in the turbine rotor through the use of a fitting piece.
German Published, Non-Prosecuted Patent Application DE 30 28 701 A1 discloses a lock for turbine blading in which moving blades are inserted in a form-locking manner in the circumferential slot of the turbine rotor and the circumferential slot may be undercut in any shape on both sides. A form-locking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a force-locking connection, which locks the elements together by force external to the elements. At least one entry point is provided on the periphery of the turbine rotor, in which a filling piece is inserted, form-locking with the blade root. A wall of the entry point or gate in the turbine rotor and that side of the filling piece which faces the wall are constructed in such a way as to be inclined at an angle to the blade axis. The closure between the wall of the entry point and the side of the filling piece is effected with a fitting piece which sits tightly in position.
The known lock is suitable in particular for root forms of the moving blades in which the blade roots are fully supported in the axial direction of the turbine rotor at the circumferential slot, for example for hammer-head roots. If the blade root is not fully supported in the axial direction in the circumferential slot, for example in the case of fir-tree or pine-tree roots, the blade root in the lock region may yield to an excessive degree when the filling piece is installed, so that the requisite prestress cannot be produced in the lock. Without prestressing of the lock assembly, the centrifugal-force effect on the inclined side of the lock during operation may not adequately clamp the fitting piece, so that the fitting piece becomes detached from the lock and the lock fails.